U.S. patent number 4,814,228 [Application Number 07/028,354] was granted by the patent office on 1989-03-21 for wet spun hydroxyethylated polybenzimidazole fibers.
This patent grant is currently assigned to Hoechst Celanese Corporation. Invention is credited to Frank J. Onorato, Michael J. Sansone, Arthur Schlask.
United States Patent |
4,814,228 |
Onorato , et al. |
March 21, 1989 |
Wet spun hydroxyethylated polybenzimidazole fibers
Abstract
Hydroxyethylated polybenzimidazole fibers are produced by a wet
jet/wet spinning or by a dry jet/wet spinning process. A spinning
solution of hydroxyethylated polybenzimidazole is extruded
vertically downward through a spinneret into a liquid coagulation
bath. The resulting fibers have pore sizes ranging from about 5
angstroms up to about 100 angstroms and are quite useful as ultra
filters for molecules with a broad range of molecular weight.
Inventors: |
Onorato; Frank J.
(Phillipsburg, NJ), Sansone; Michael J. (Berkeley Heights,
NJ), Schlask; Arthur (Roselle Park, NJ) |
Assignee: |
Hoechst Celanese Corporation
(Somerville, NJ)
|
Family
ID: |
21842986 |
Appl.
No.: |
07/028,354 |
Filed: |
March 20, 1987 |
Current U.S.
Class: |
428/398;
210/500.23; 210/500.28; 264/183; 264/184; 264/210.8; 264/41;
428/376 |
Current CPC
Class: |
B01D
69/08 (20130101); B01D 71/62 (20130101); D01D
5/24 (20130101); D01F 6/74 (20130101); Y10T
428/2975 (20150115); Y10T 428/2935 (20150115) |
Current International
Class: |
B01D
69/08 (20060101); B01D 69/00 (20060101); B01D
71/00 (20060101); B01D 71/62 (20060101); C12M
3/06 (20060101); D01F 6/74 (20060101); D01D
5/00 (20060101); D01D 5/24 (20060101); D01F
6/58 (20060101); D02G 003/00 () |
Field of
Search: |
;428/364,392,397,398,376
;264/183,184,41,210.8 ;210/500.28 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kendell; Lorraine T.
Attorney, Agent or Firm: Lynch, Cox, Gilman & Mahan
Claims
We claim:
1. A porous hydroxyethylated polybenzimidazole fiber with pore
sizes ranging from about 5 to 100 angstroms produced by the process
comprising the steps of:
(a) forming a solution of a polybenzimidazole polymer wherein the
concentration of the polybenzimidazole in the solution ranges from
about 15 to about 25 percent by weight based upon the total weight
of the solution;
(b) reacting the polybenzimidazole polymer with an ethylene
carbonate wherein the ratio of the ethylene carbonate reactive
groups to the polybenzimidazole imidazole hydrogen sites is at
least stoichiometric to form at least about a 20 percent
substituted hydroxyethylated polybenzimidazole polymer
solution;
(c) extruding the hydroxyethylated polybenzimidazole polymer
solution through a spinneret into a gaseous atmosphere wherein the
extrusion orifices of the spinneret are located approximately 1/8
of an inch to about 10 inches above the coagulation bath; and
(d) coagulating the extruded hydroxyethylated polybenzimidazole
solution in a coagulation bath comprised of at least about 60
percent by weight of a non-solvent based upon the total weight of
the solution, and from 0 to 40 percent [N,N-dimethylacetamide] by
weight of a solvent based upon the total weight of the solution,
wherein the coagulation bath is maintained at a temperature of at
least 45.degree. C. to form porous hydroxyethylated
polybenzimidazole fibers with a pore size of from about 5 to about
100 angstroms.
2. The fibers of claim 1 wherein the polybenzimidazole polymer
starting material is characterized by recurring monomeric units of:
##STR9## where R is a tetravalent aromatic nucleus with the
nitrogen atoms forming the benzimidazole rings being paired upon
adjacent carbon atoms, and R' is a divalent substituent selected
from aliphatic, alicyclic and aromatic radicals containing between
about 2 and
3. The fiber of claim 1 wherein the polybenzimidazole polymer
starting material is comprised of recurring monomeric units of:
##STR10## wherein the Z is an aromatic nucleus having the nitrogen
atoms forming the benzimidazole ring paired upon adjacent carbon
atoms of the aromatic nucleus.
4. The fiber of claim 1 wherein the polybenzimidazole starting
material is poly-2,2'(m-phenylene)-5,5'-bibenzimidazole.
5. The fiber of claim 1 wherein one or both of the alkyl sites on
the ethylene carbonate is substituted by a monovalent member
selected from the group consisting of hydrogen, unsubstituted
alkyl, substituted alkyl, aryl or substituted aryl
substituents.
6. The fiber of claim 1 wherein the alkyl sites on the ethylene
carbonate are unsubstituted.
7. The fiber of claim 1 wherein the ratio of carbonate reactive
groups to each reactive imidazole group is from about 10:1 to
20.1.
8. The fiber of claim 1 wherein the ethylene carbonate reaction is
conducted at a temperature between about 145.degree. C. and about
210.degree. C. for a period of about 3 to about 5 hours.
9. The fiber of claim 1 wherein from about 50 to about 70 percent
of the reactive imidazole hydrogen sites are substituted with
hydroxyethyl substituents.
10. The fiber of claim 1 wherein the viscosity of the
hydroxyethylated polybenzimidazole polymer solution is from about
200 to about 2500 posies at 30.degree. C.
11. The fiber of claim 1 wherein the concentration of the
hydroxyethylated polybenzimidazole formed in the solution is from
about 20 to about 30 percent by weight based on the total solution
weight.
12. The fiber of claim 1 wherein the hydroxyethylated
polybenzimidazole polymer solution contains about 1 to about 5
percent lithium chloride, based upon the weight of the
hydroxyethylated polybenzimidazole in the solution.
13. The fiber of claim 1 wherein the non-solvent is selected from a
group consisting of water, ethylene glycol, sulfuric acid, C.sub.1
-C.sub.6 alkyl alcohols and combinations thereof.
14. The fiber of claim 1 wherein the non-solvent is C.sub.1 to
C.sub.6 alkyl alcohol.
15. The fiber of claim 1 wherein the solvent in the coagulation
bath is comprised of N,N-dimethylacetamide.
16. The fiber of claim 1 wherein it is drawn in a draw ratio from
about 2:1 to about 10:1.
17. A porous hydroxyethylated polybenzimidazole fiber wherein the
pore size of the fiber ranges from about 5 angstroms to about 100
angstroms.
Description
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to substituted polybenzimidazole articles
and the process for their production. More particularly the
invention relates to hydroxyethylated polybenzimidazole fibers and
the process for their production.
2. Prior Art
Polybenzimidazoles are a known class of heterocyclic polymers which
are characterized by a high degree of thermal and chemical
stability. Processes for their production are disclosed in U.S.
Pat. No. Re. 26,065, and U.S. Pat. Nos. 3,313,783, 3,509,108,
3,555,389, 3,433,772, 3,408,336, 3,549,603, 3,708,439, 4,154,919,
and 4,312,976. (All patents enumerated hereof are incorporated by
reference.)
Fibers produced from polybenzimidazole polymers retain these
favorable attributes and can be useful in a broad range of
applications. For example, polybenzimidazole filaments have been
utilized for electrodialysis, reverse osmosis, and for a wide range
of other separatory uses. However, because the pore size of
unsubstituted polybenzimidazole fibers is quite small, i.e. less
than about 1 angstrom, polybenzimidazole fibers are not useful as
filters for molecules having molecular weights greater than about
1000.
Further, although polybenzimidazole polymers are generally
resistant to chemical reaction, the imidazole nitrogen-hydrogen
bond on the polybenzimidazole polymer is susceptible to reaction
under certain conditions.
Polybenzimidazole fibers have been produced by two basic processes.
The first is dry spinning, which involves spinning a
polybenzimidazole solution through a spinneret into an evaporative
chamber. The second is wet spinning wherein the spinning solution
is spun through a spinneret either directly into a coagulation
bath, "wet jet/wet spinning", or through an air gap into the
coagulation bath, "dry jet/wet spinning".
Typical dry spinning procedures are disclosed in U.S. Pat. Nos.
3,584,104 and 3,502,756 while typical wet spinning processes are
disclosed in U.S. Pat. Nos. 4,512,894, 4,263,245, 3,851,025,
3,619,453, 3,526,693 and 3,441,640. While the processes and the
products produced by these processes vary based on such differences
as the composition of the coagulating bath, the denier of the spun
fiber, or the structure of the fiber, none of these patents
discloses a method for spinning fibers formed from substituted
polybenzimidazole polymers, in general, or hydroxyethylated
polybenzimidazole polymers, in particular.
While processes for the production of substituted polybenzimidazole
fibers have not been disclosed, several processes for the
production of substituted polybenzimidazole polymers have been
disclosed. For example, U.S. Pat. No. 3,578,644 discloses a process
for the production of an hydroxyl modified polybenzimidazole
polymer produced by reacting a polybenzimidazole polymer with an
omega-halo-alkanol or a 1,2-alkylene oxide in the presence of a
basic catalyst such as sodium hydride. However, this reaction
process results in the formation of undesirable organic salts as a
by-product; requires a pressurized vessel for the reaction; and the
types of polybenzimidazole polymers which can be used in this
reaction are limited. For example, such polybenzimidazole polymers
as poly-2,2'(m-phenylene)-5,5'-bibenzimidazole and other similarly
structured polybenzimidazole polymers may not be used because the
bridging groups between the reactive imidazole rings are sterically
hindered, thereby severely restricting the reactivity of the
imidazole nitrogens. Further, the '644 patent fails to disclose any
process for the production of hydroxyl modified polybenzimidazole
fibers, membranes or other shaped articles.
An additional process for the production of hydroxyl modified
polybenzimidazole is disclosed in U.S. Pat. No. 4,599,388.
Further processes for the production of substituted
polybenzimidazoles are disclosed in U.S. Pat. Nos. 4,579,915,
4,377,546, 3,943,125 and 3,518,234. U.S. Pat. No. 4,579,915,
discloses substituted polybenzimidazole polymers wherein the
imidazole hydrogen is replaced by an aromatic substituent
corresponding to the formula: ##STR1## where R is nitro, cyano, or
trifluoromethyl and R' is hydrogen, alkyl, nitro, cyano or
trifluoromethyl.
U.S. Pat. No. 4,377,546 discloses a phenol substituted
polybenzimidazole but does not disclose a process for its
preparation.
U.S. Pat. No. 3,943,125 discloses a broad range of substituted
tetraamino heterocyclic compounds useful in the preparation of
substituted polybenzimidazoles. However, the patent fails to
disclose hydroxyethylated polybenzimidazole polymers or a process
for the production of hydroxyethylated polybenzimidazole
articles.
U.S. Pat. No. 3,518,234 discloses N-aryl substituted
polybenzimidazole polymers but, again, fails to disclose
hydroxyethylated polybenzimidazole polymers or a process for the
production of hydroxyethylated polybenzimidazole articles.
Accordingly, it is an object of the present invention to prepare
hydroxyethylated polybenzimidazole fibers.
It is a further object of this invention is to prepare
hydroxyethylated polybenzimidazole fibers that exhibit a high
degree of chemical and thermal stability.
It is a further object of this invention to prepare
hydroxyethylated polybenzimidazole ultra filters which can filter a
broad range of molecular weight compounds.
These and other objects, as well as the scope, nature, and
utilization of the process will be apparent from the following
description and the appended claims.
SUMMARY OF INVENTION
In accordance with the present invention there is provided an
hydroxyethylated polybenzimidazole fiber which is prepared by the
following process:
a. forming a solution of a polybenzimidazole polymer;
b. reacting the polybenzimidazole polymer with an ethylene
carbonate to form an hydroxyethylated polybenzimidazole polymer
solution;
c. extruding the hydroxyethylated polybenzimidazole polymer
solution through a spinneret; and
d. coagulating the hydroxyethylated polybenzimidazole polymer
solution in a coagulation bath to form hydroxyethylated
polybenzimidazole fibers.
The fibers produced by this process can be utilized as separatory
media for such uses as ultra filters which exhibit a broad range of
molecular weight cut offs. They may also be used for the production
of high strength, chemically resistant, separatory articles where
the relatively large micropore size of the articles would be
useful.
DETAILED DESCRIPTION OF INVENTION
A. The Starting Material
The polybenzimidazole starting materials are a known class of
heterocyclic polymers which are characterized by a recurring
monomer unit which corresponds to the following Formula I or II.
Formula I is: ##STR2## where R is a tetravalent aromatic nucleus
with the nitrogen atoms forming the benzimidazole rings being
paired upon adjacent carbon atoms, i.e., ortho carbon atoms, of the
aromatic nucleus, and R' is a divalent substituent selected from
aliphatic, alicyclic and aromatic radicals. Illustrative of R'
substituents are divalent organic radicals containing from about 2
to about 20 carbon atoms, such as ethylene, propylene, butylene,
cyclohexylene, phenylene, pyridine, pyrazine, furan, thiophene,
pyran, and the like.
Formula II corresponds to the structure: ##STR3## where Z is an
aromatic nucleus having the nitrogen atom forming the benzimidazole
ring paired upon adjacent carbon atoms of the aromatic nucleus.
The above illustrated polybenzimidazoles can be prepared by various
known processes, as described in the Background of Invention
section.
The following generalized equation illustrates the condensation
reaction which occurs in forming the polybenzimidazoles having the
recurring units of Formula I. ##STR4##
Such polybenzimidazoles are produced by the reaction of a mixture
of (1) at least one aromatic tetraamine containing two groups of
amine substituents, the amine substituents in each group being in
an ortho position relative to each other, and (2) at least one
dicarboxylate ester in which R.sup.1 and R.sup.2 in the compounds
shown are substituents selected from aliphatic, alicyclic and
aromatic groups.
Examples of polybenzimidazoles which have the recurring structure
of Formula I include:
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole;
poly-2,2'-(pyridylene-3",5")-5,5'-bibenzimidazole;
poly-2,2'-(furylene-2",5")-5,5'-bibenzimidazole;
poly-2,2'-(naphthalene-1",6")-5,5'-bibenzimidazole;
poly-2,2'-(bihenylene-4",4")-5,5'-bibenzimidazole;
poly-2,2'-amylene-5,5'-bibenzimidazole;
poly-2,2'-octamethylene-5,5'-bibenzimidazole;
poly-2,6'-(m-phenylene)-diimidazobenzene;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)ether;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)sulfide;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)sulfone;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)methane;
poly-2',2"-(m-phenylene)-5',5"-di(benzimidazole)-propane-2,2;
and
poly-2,2'-(m-phenylene)-5',5"-di(benzimidazole)-ethylene-1,2.
The preferred polybenzimidazole of Formula I is
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole as characterized by
the recurring monomeric unit: ##STR5##
The polybenzimidazoles having the recurring monomer unit of Formula
II can be prepared by the autocondensation of at least one aromatic
compound having a pair of amine substituents in an ortho position
relative to each other and a carboxylate ester group positioned
upon an aromatic nucleus. Examples of such compounds are esters of
diaminocarboxylic acids which include 3,4-diaminonaphthalene acid;
5,6-diaminonaphthalene-1-carboxylic acid;
5,6-diamino-naphthalene-2-carboxylic acid;
6,7-diaminonaphthalene-1-carboxylic acid;
6,7-diaminonaphthalene-2-carboxylic acid;, and the like. A
preferred compound is 4-phenoxycarbonyl-3',4'-diaminodiphenyl
ether: ##STR6## The polymer obtained with
4-phenoxycarbonyl-3',4'-diaminodiphenyl ether is
poly-5-(4-phenyleneoxy)benzimidazole.
A polybenzimidazole starting material for the present invention
process typically will exhibit an inherent viscosity between about
0.1 and about 1.0 dl/g when measured at a concentration of 0.4 g of
said polybenzimidazole in 100 ml of 97 percent sulfuric acid at
25.degree. C.
The weight average molecular weight of a typical polybenzimidazole
starting material will be in the range between about 1000 and about
100,000.
B. The Carbonate Reaction
The above polybenzimidazole starting material is reacted with a
cyclic carbonate in an organic solvent medium to produce the
desired hydroxyethylated polybenzimidazole polymer. The cyclic
carbonate is of the following general formula: ##STR7## wherein R
is a C.sub.2 -C.sub.6 alkyl group. One or more of the alkyl sites
may be substituted by a monovalent member selected from the group
consisting of hydrogen, alkyl, substituted alkyl, aryl or
substituted aryl substituents. In a preferred embodiment the cyclic
carbonate is an ethylene carbonate, and one or both of the alkyl
sites on the ethylene carbonate may be substituted by a monovalent
member selected from the group consisting of hydrogen unsubstituted
alkyl, substituted alkyl, aryl or substituted aryl substituents. In
a preferred embodiment the alkyl sites are unsubstituted.
The carbonate reactant can be employed essentially in any molar
quantity with respect to the polybenzimidazole starting material to
produce various percentages of substitution. Preferably, the
carbonate reactant is employed in at least a stoichiometric
quantity with respect to the reactive imidazole hydrogen sites on
the polybenzimidazole polymer. In a preferred embodiment, the ratio
of carbonate reactant groups to each reactive imidazole group is
from about 10 to about 20 to 1. It is desirable to achieve at least
about a 20 percent substitution of the reactive imidazole hydrogen
sites with the hydroxyalkyl group. In a preferred embodiment,
substitutions of at least about 50 to 70 percent should be
obtained.
The hydroxyalkylation reaction between the cyclic carbonate and
polybenzimidazole typically is conducted at a temperature between
about 30.degree. C. and about 225.degree. C. for a reaction period
between about 0.5 and about 24 hours. The reaction can be
accomplished conveniently at ambient pressures. In a preferred
embodiment the reaction is conducted at a temperature between about
145.degree. C. and about 210.degree. C. for about 3 to about 5
hours.
The concentration of the polybenzimidazole and cyclic carbonate
reactants in the organic solvent reaction medium is limited only by
the solubility of the polybenzimidazole in the solvent. Generally,
the polybenzimidazole concentration in the organic solvent medium
will be in the range between about 1 to about 30 percent by weight,
based on the total weight of the reaction solution. The molecular
weight of the polybenzimidazole is a factor in determining the
maximum solute weight of the polymer in the organic solvent
reaction medium. In a preferred embodiment polybenzimidazole dopes
of about 15 to about 25 percent by weigh based on the total
solution weight are used.
Organic solvents suitable for purposes of the present invention
include N,N-dimethylformamide, N,N-dimethylacetamide,
dimethylsulfoxide, N-methyl-2-pyrrolidone, and the like with the
preferred solvent being N,N-dimethylacetamide.
When unsubstituted ethylene carbonate is used as a reactant, the
substituted polybenzimidazole produced is hydroxyethylated
polybenzimidazole according to the following reaction scheme:
##STR8## The (I) and (II) repeating units correspond to the Formula
I and Formula II structures as previously defined.
After the reaction process is completed, the hydroxyalkyl
substituted polybenzimidazole can be recovered by any conventional
procedures, such as by vacuum distillation of the solvent medium to
provide a residual polymeric solid, or by precipitation of the
polymer from the solvent medium by addition of a non-solvent such
as acetone, methanol or hexane. The substituted polybenzimidazole
polymer of the present invention can also be spun into fibers or
cast into membranes.
C. Fiber Formation
To prepare the hydroxyethylated polybenzimidazole fibers, the
hydroxyethylated polybenzimidazole polymer prepared by the
proceeding procedure is mixed with a solvent to produce a spinning
solution. Although the amount of hydroxyethylated polybenzimidazole
polymer solids which can be used is dependent upon the viscosity
and molecular weight of the particular hydroxyethylated
polybenzimidazole polymer, polymer concentrations in the range of
about 1 to about 30 percent, by weight based on the total solution
weight, are typically used, with polymer concentrations in the
range of about 20 to about 30 percent preferred. A minor amount of
lithium chloride may also be added to prevent phase separation
(i.e. about 1 to about 5 percent by weight based on the weight of
the hydroxyethylated polybenzimidazole in the solution). Suitable
solvents for preparation of the spinning solution include those
solvents which are commonly used in preparing the polybenzimidazole
polymer solution for reaction with ethylene carbonate including
N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide,
and N-methyl-2-pyrrolidone, with N,N-dimethylacetamide being the
preferred solvent.
The viscosity of the hydroxyethylated polybenzimidazole polymer
solvent solution can range from about 200 to about 2500 poises at
30.degree. C. because of the variations in percentage of
substitution of the hydroxyethylated polybenzimidazole polymer and
the molecular weight of the particular hydroxyethylated
polybenzimidazole polymer. In selecting the hydroxyethylated
polybenzimidazole dope to be used, it is desirable that the dope
have the highest possible viscosity which can still easily be
extruded under the desired extrusion conditions. In addition to
variations in the fibers caused by different viscosities and
percentages of solid content, the characteristics of both the
spinning solution and the resulting spun fibers will also vary
considerably depending on the percentage of substitution of the
precursor hydroxyethylated polybenzimidazole polymer. Useful
filaments are produced from hydroxyethylated polybenzimidazole
polymers wherein the substitutions are greater than about 20
percent. In a preferred embodiment, a 50 to 70 percent substituted
hydroxyethylated polybenzimidazole spinning solution is used.
Using conventional equipment and techniques, a spinning solution of
the hydroxyethylated polybenzimidazole is placed in an extrusion or
spinning bomb. The bomb, containing the spinning dope, is attached
to a conventional spinneret and is pressurized with sufficient
pressure to cause the polymer solution contained in the bomb to
escape through the spinneret jet. It is, of course, understood that
in order to prepare optimum fibers, the dope placed in the bomb
should be filtered either prior to placing it in the bomb or just
prior to spinning.
The hydroxyethylated polybenzimidazole polymer is preferably
introduced and maintained in the spinning bomb at about room
temperature (i.e. from about 15.degree. C. to about 35.degree. C.)
The spinning solution is extruded through a plurality of extrusion
orifices (any reasonable number of orifices from 1 to several
hundred is acceptable). The orifices of the present invention can
have a diameter of from approximately 20 to 500 microns.
The fibers may be spun through conventional extrusion orifices to
produce solid, non-hollow fibers or, in an alternative embodiment,
the fibers may be hollow. The spinneret through which the hollow
fibers are spun is referred to as a concentric hollow jet
spinneret, and is comprised of an inner nozzle and a concentric
outer nozzle arranged about the inner nozzle. In order to maintain
the hollow configuration of spun fibers during the spinning
process, a fluid, either gaseous or liquid, is forced through the
inner nozzle at a pressure of about 15 p.s.i. Examples of this
fluid include nitrogen and ethylene glycol. The hollow
hydroxyethylated polybenzimidazole fibers produced in the present
process commonly have an outer diameter of about 50 to about 500
microns and an inner diameter of about 20 to about 350 microns. In
a preferred embodiment, hollow hydroxyethylated polybenzimidazole
fibers produced in the present process have an outer diameter of
about 130 to 300 microns and a wall thickness of about 40 to 90
microns.
As the hydroxyethylated polybenzimidazole polymer is spun, it is
fed into a coagulation bath. Although the filaments can be spun
directly into the coagulation bath by locating the spinneret within
the coagulation bath, it is preferred to expose the as-spun fibers
to a gaseous environment to effect partial surface coagulation by
allowing them to drop freely for a short distance prior to entering
the coagulation bath. The distance between the face of the
spinneret and the coagulation bath, known as the "air gap", may
influence the composition of fibers. For example, large air gaps
increase the amount of surface coagulation. Air gaps suitable for
use in the present invention range from approximately 1/8 inch to
about 10 inches and preferably from approximately 1/2 inch to about
5 inches. When using this dry jet/wet spinning method, the gaseous
atmosphere through which the fibers are spun may be composed of any
dry inert gas such as nitrogen, the noble gases such as argon,
steam, combustion gases such as carbon dioxide, with nitrogen as
the preferred gas. The temperature of the gaseous atmosphere will
depend on the extent of coagulation of the fibers desired during
the air gap drop. When a high temperature gaseous atmosphere is
used (i.e. above about 150.degree. C.), the coagulation of as-spun
fibers occurs rapidly and a barrier layer may form on the surface
of the fiber reducing its porosity. Accordingly, in a preferred
embodiment, the temperature of the gaseous atmosphere is maintained
at about 55.degree. C. to about 120.degree. C.
Vapors from the coagulation bath may also be introduced into the
gaseous atmosphere of the column to prevent the formation of a
barrier layer and enhance pore formation on the surface of the
fibers. If vapors are used, at some point the temperature of the
surface of the as-spun fibers must be less then the dew point of
the non-solvent vapor within the column. This allows the vapors to
condense on the surface of the as-spun fibers and enhance the
microporosity of the fibers.
After extrusion, the filaments are passed through a liquid
coagulation bath. The coagulation bath may include any of the
non-solvent coagulants commonly used in the coagulation baths for
unsubstituted polybenzimidazole fibers such as water, ethylene
glycol and sulfuric acid, either alone or in combinations.
Additional acceptable non-solvent coagulants may include any of the
C.sub.1 to C.sub.6 alkyl alcohols, such as methanol. In addition,
certain solvents for the hydroxyethylated polybenzimidazole such as
N,N-dimethylacetamide may be included in the coagulation bath. By
varying the composition of the coagulating bath, the average pore
size of the fiber can be requested. For example, when higher
percentages of water are used in the coagulating bath, the average
pore sizes on the surface of the as-spun fibers may be as small as
5 angstroms. However, by adding to the coagulating bath up to about
40 percent of a solvent for the hydroxyethylated polybenzimidazole,
the average pore size on the surface of the as-spun
hydroxyethylated polybenzimidazole fibers increases to about 100
angstroms. Coagulation baths containing percentages of a solvent
for hydroxyethylated polybenzimidazole above about 40 percent fail
to adequately coagulate the as-spun hydroxyethylated
polybenzimidazole into well formed fibers. In a preferred
embodiment the coagulation bath is comprised of at least about 60
percent, by weight based upon the total weight of the bath, of a
non-solvent for the hydroxyethylated polybenzimidazole polymer and
about 0 to about 40 percent, by weight based upon the total weight
of the bath, of a solvent for the hydroxyethylated
polybenzimidazole polymer, and most preferably 60 percent methanol
and 40 percent N,N-dimethyl acetamide.
Although a wide range of bath temperatures may be employed, an
increase in the microporosity of the fibers occurs when the
temperature of the bath is maintained above that normally used for
the coagulation of smooth skin, unsubstituted, polybenzimidazole
fibers. Bath temperatures ranging above about 25.degree. C. and
preferably above about 45.degree. C. up to the boiling point of the
coagulant, and more preferably from about 45.degree. C. to about
55.degree. C., will assist in the formation of micropores in the
hydroxyethylated polybenzimidazole fibers. By carefully controlling
both the composition of the coagulation bath and the temperature of
the coagulation bath, the size of the micropores in the
hydroxyethylated polybenzimidazole fibers can be closely
controlled. For example, if an hydroxyethylated polybenzimidazole
fiber with pore sizes ranging from about 1 angstrom to about 10
angstrom is desired, the coagulation bath should principally be
comprised of water maintained at a relatively cool temperature of
about 15.degree. C. to about 30.degree. C. However, if larger size
pores are desired, for example, above about 70 angstroms, the
coagulation bath should be comprised of about 25 to about 40
percent a solvent for the hydroxyethylated polybenzimidazole, such
as N,N-dimethylacetamide, and the temperature of the coagulation
bath should be maintained above about 45.degree. C. and preferably
from about 45.degree. C. to about 100.degree. C.
During the coagulation process, a slight flow of the coagulant is
continually introduced into the coagulation bath to prevent a build
up of the solvent which has been removed from the extruded
filament.
During the spinning process the fibers may be drawn at a draw ratio
of about 1.2:1 to about 3:1 while dropping through the air gap.
Further drawing may occur while the fibers are being passed through
the coagulation bath. The total draw ratio during spinning and
coagulation can range from approximately 1.5:1 to about 50:1, with
a preferable total draw ratio of about 2:1 to about 10:1.
The hydroxyethylated polybenzimidazole fibers may additionally be
heat drawn after coagulation. If the filaments are heat drawn, it
is preferably accomplished by passing the dry fibers through a
drawing furnace at temperatures of approximately 400.degree. C. to
about 500.degree. C. for about 1 to 5 minutes. The tension on the
filament is maintained so that the total heat draw ratio is
approximately 1:5 to 1 to about 10:1.
D. Post Coagulation Treatment
The coagulated fibers leaving the coagulation bath are next passed
to a washing zone. The continuous length of the hydroxyethylated
polybenzimidazole fibers is washed to remove, at least, the major
portion of the residual spinning solvent. Typically a simple warm
water washing is employed; however, if desired, other wash
materials such as acetone, methanol, methylethyl ketone and similar
solvent miscible, organic solvents may be used in place of or in
combination with warm water. Although a wide range of temperatures
may be employed, in the bath, the wash liquid is preferably
provided at a temperature of approximately 55.degree. C. to about
65.degree. C.
If desired, the hydroxyethylated polybenzimidazole fibers may be
annealed. The annealing process may increase the tightness of the
fibers and broaden the cut off range of molecular weights of the
fibers. If the fibers are annealed, they may be annealed using any
conventional annealing process for unsubstituted polybenzimidazole
fibers, such as is disclosed in U.S. Pat. No. 4,512,894, which is
incorporated by reference.
The fibers are collected by any conventional means, with the
preferred apparatus being assembled from a D.C. motor, whose speed
can be precisely controlled, and a transverse winder. This
arrangement provides less tension during take up and permits longer
continuous operation without breaking the fibers.
It has been surprisingly discovered that the resulting
hydroxyethylated polybenzimidazole fibers formed are significantly
different from unsubstituted polybenzimidazole fibers. For example,
while the pore size of unsubstituted polybenzimidazole fibers is
less than about 1 angstrom, hydroxyethylated polybenzimidazole
fibers, depending upon the coagulation bath composition and
temperature, are characterized by pore sizes ranging from about 5
angstroms to about 100 angstroms.
Because of the relatively large pore size and the large range of
pore sizes that are available, the fibers can be utilized as ultra
filters for compounds with a large range of molecular weights.
Filters produced from these fibers can have molecular weight cut
offs as low as about 1,000 or as high as about 50,000.
Fibers produced by this process may also be used as bioreactors for
large molecular weight proteins which are grown on the outer
surface of the fibers. These proteins can be fed by nutrient
solutions running through the lumen of hollow, hydroxyethylated
polybenzimidazole fibers. The nutrients freely flow through the
pores of the ultra filter to feed the proteins, while the large
molecular weight proteins would be prevented from passing through
the pores into the lumen.
The following examples are given as specific illustrations of the
invention. All parts and percentages are by weight unless otherwise
stated. It should be understood however, that the invention is not
limited to the specific details set forth in the examples.
EXAMPLE 1
A polybenzimidazole starting solution was prepared by stirring 100
grams of poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole polymer in
particulate form, with 450 grams of N,N-dimethylacetamide and 5
grams of lithium chloride for five hours under argon gas in a 1000
ml stainless steel Hoke bomb at 230.degree. C. The solution was
then filtered to remove any residual solids. The solution was
transferred to a 3 neck, round bottom flask, fitted with a reflux
condenser, a mechanical stirrer, and a thermometer, and 28 grams of
98 percent pure ethylene carbonate were added. The reaction flask
was heated to 160.degree. C. and held at that temperature for 5
hours. The solution was then cooled to room temperature and added
to 1500 grams of acetone to precipitate out the resultant solids,
which were then air dried. Analysis disclosed the presence of 117
grams of hydroxyethylated polybenzimidazole, with a percentage of
substitution of about 61 percent.
EXAMPLE 2
100 grams of the 61 percent substituted hydroxyethylated
polybenzimidazole particulate produced from the reaction of Example
1 was disolved along with 5 grams of lithium chloride in 295 grams
of N,N-dimethylacetamide to form a spinning solution. The spinning
solution was placed in a conventional reservoir which was
maintained at room temperature, (i.e. about 25.degree. C.) and
extruded vertically downwardly through a hollow fiber spinneret,
having an outside diameter of 500 .mu.m and an inside diameter of
350 .mu.m. for an angular thickness of 75 .mu.m. The bore diameter
was 175 .mu.m. The extruded hydroxyethylated polybenzimidazole
polymer was passed through a 1 in. air gap into a conventional 1
meter coagulation bath containing water at a temperature of
30.degree. C. The coagulation bath was continually fed with a
slight flow of fresh water to prevent a build up of solvents as the
spinning progressed. After coagulation, the fibers were taken up at
a speed of 0.64 centimeters per second on a conventional take-up
bobbin and immersed in a wash bath containing continuously running
warm water (at a temperature of approximately 55.degree. C. to
65.degree. C.) for 10 minutes. The resulting fibers, when tested,
exhibited a molecular weight cut off of about 20,000.
As is apparent from these examples, hydroxyethylated
polybenzimidazole fibers produced by the instant invention have
pore sizes significantly larger than those of unsubstituted
polybenzimidazole fibers.
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